| 1. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
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Impedance Spectroscopy Modeling of Nickel–Molybdenum Alloys on Porous and Flat Substrates for Applications in Water Splitting
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:39, s. 23890-23897
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen production by splitting water using electrocatalysts powered by renewable energy from solar or wind plants is one promising alternative to produce a carbon-free and sustainable fuel. Earth-abundant and nonprecious metals are, here, of interest as a replacement for scarce and expensive platinum group catalysts. Ni–Mo is a promising alternative to Pt, but the type of the substrate could ultimately affect both the initial growth conditions and the final charge transfer in the system as a whole with resistive junctions formed in the heterojunction interface. In this study, we investigated the effect of different substrates on the hydrogen evolution reaction (HER) of Ni–Mo electrocatalysts. Ni–Mo catalysts (30 atom % Ni, 70 atom % Mo) were sputtered on various substrates with different porosities and conductivities. There was no apparent morphological difference at the surface of the catalytic films sputtered on the different substrates, and the substrates were classified from microporous to flat. The electrochemical characterization was carried out with linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in the frequency range 0.7 Hz–100 kHz. LSV measurements were carried out at direct current (DC) potentials between 200 and −400 mV vs the reversible hydrogen electrode (RHE) in 1 M NaOH encompassing the HER. The lowest overpotentials for HER were obtained for films on the nickel foam at all current densities (−157 mV vs RHE @ 10 mA cm–2), and the overpotentials increased in the order of nickel foil, carbon cloth, fluorine-doped tin oxide, and indium tin oxide glass. EIS data were fitted with two equivalent circuit models and compared for different DC potentials and different substrate morphologies and conductivities. By critical evaluation of the data from the models, the influence of the substrates on the reaction kinetics was analyzed in the high- and low-frequency regions. In the high-frequency region, a strong substrate dependence was seen and interpreted with a Schottky-type barrier, which can be rationalized as being due to a potential barrier in the material heterojunctions or a resistive substrate–film oxide/hydroxide. The results highlight the importance of substrates, the total charge transfer properties in electrocatalysis, and the relevance of different circuit components in EIS and underpin the necessity to incorporate high-conductivity, chemically inert, and work-function-matched substrate–catalysts in the catalyst system.
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| 2. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
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NiMoV and NiO-based catalysts for efficient solar-driven water splitting using thermally integrated photovoltaics in a scalable approach
- 2021
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Ingår i: iScience. - : Cell Press. - 2589-0042. ; 24:1
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a trimetallic NiMoV catalyst is developed for the hydrogen evolution reaction and characterized with respect to structure, valence, and elemental distribution. The overpotential to drive a 10 mA cm−2 current density is lowered from 94 to 78 mV versus reversible hydrogen electrode by introducing V into NiMo. A scalable stand-alone system for solar-driven water splitting was examined for a laboratory-scale device with 1.6 cm2 photovoltaic (PV) module area to an up-scaled device with 100 cm2 area. The NiMoV cathodic catalyst is combined with a NiO anode in alkaline electrolyzer unit thermally connected to synthesized (Ag,Cu) (In,Ga)Se2 ((A)CIGS) PV modules. Performance of 3- and 4-cell interconnected PV modules, electrolyzer, and hydrogen production of the PV electrolyzer are examined between 25°C and 50°C. The PV-electrolysis device having a 4-cell (A)CIGS under 100 mW cm−2 illumination and NiMoV-NiO electrolyzer shows 9.1% maximum and 8.5% averaged efficiency for 100 h operation.
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| 3. |
- Fan, Lizhou, et al.
(författare)
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Molecular Functionalization of NiO Nanocatalyst for Enhanced Water Oxidation by Electronic Structure Engineering
- 2020
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 13:22, s. 5901-5909
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Tidskriftsartikel (refereegranskat)abstract
- Tuning the local environment of nanomaterial-based catalysts has emerged as an effective approach to optimize their oxygen evolution reaction (OER) performance, yet the controlled electronic modulation around surface active sites remains a great challenge. Herein, directed electronic modulation of NiO nanoparticles was achieved by simple surface molecular modification with small organic molecules. By adjusting the electronic properties of modifying molecules, the local electronic structure was rationally tailored and a close electronic structure-activity relationship was discovered: the increasing electron-withdrawing modification readily decreased the electron density around surface Ni sites, accelerating the reaction kinetics and improving OER activity, and vice versa. Detailed investigation by operando Raman spectroelectrochemistry revealed that the electron-withdrawing modification facilitates the charge-transfer kinetics, stimulates the catalyst reconstruction, and promotes abundant high-valent gamma-NiOOH reactive species generation. The NiO-C(6)F(5)catalyst, with the optimized electronic environment, exhibited superior performance towards water oxidation. This work provides a well-designed and effective approach for heterogeneous catalyst fabrication under the molecular level.
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| 4. |
- Kristanl, Matej, et al.
(författare)
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The Seventh Visual Object Tracking VOT2019 Challenge Results
- 2019
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Ingår i: 2019 IEEE/CVF INTERNATIONAL CONFERENCE ON COMPUTER VISION WORKSHOPS (ICCVW). - : IEEE COMPUTER SOC. - 9781728150239 ; , s. 2206-2241
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Konferensbidrag (refereegranskat)abstract
- The Visual Object Tracking challenge VOT2019 is the seventh annual tracker benchmarking activity organized by the VOT initiative. Results of 81 trackers are presented; many are state-of-the-art trackers published at major computer vision conferences or in journals in the recent years. The evaluation included the standard VOT and other popular methodologies for short-term tracking analysis as well as the standard VOT methodology for long-term tracking analysis. The VOT2019 challenge was composed of five challenges focusing on different tracking domains: (i) VOT-ST2019 challenge focused on short-term tracking in RGB, (ii) VOT-RT2019 challenge focused on "real-time" short-term tracking in RGB, (iii) VOT-LT2019 focused on long-term tracking namely coping with target disappearance and reappearance. Two new challenges have been introduced: (iv) VOT-RGBT2019 challenge focused on short-term tracking in RGB and thermal imagery and (v) VOT-RGBD2019 challenge focused on long-term tracking in RGB and depth imagery. The VOT-ST2019, VOT-RT2019 and VOT-LT2019 datasets were refreshed while new datasets were introduced for VOT-RGBT2019 and VOT-RGBD2019. The VOT toolkit has been updated to support both standard short-term, long-term tracking and tracking with multi-channel imagery. Performance of the tested trackers typically by far exceeds standard baselines. The source code for most of the trackers is publicly available from the VOT page. The dataset, the evaluation kit and the results are publicly available at the challenge website(1).
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| 5. |
- Liu, Chenjuan, 1988-, et al.
(författare)
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A free standing Ru–TiC nanowire array/carbon textile cathode with enhanced stability for Li–O2 batteries
- 2018
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 6, s. 23659-23668
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Tidskriftsartikel (refereegranskat)abstract
- The instability of carbon cathode materials is one of the key problems that hinder the development of lithium–air/lithium–oxygen (Li–O2) batteries. In this contribution, a type of TiC-based cathode is developed as a suitable alternative to carbon based cathodes, and its stability with respect to its surface properties is investigated. Here, a free-standing TiC nanowire array cathode was in situ grown on a carbon textile, covering its exposed surface. The TiC nanowire array, via deposition with Ru nanoparticles, showed enhanced oxygen reduction/evolution activity and cyclability, compared to the one without Ru modification. The battery performance of the Li–O2cells with Ru–TiC was investigated by using in operando synchrotron radiation powder X-ray diffraction (SR-PXD) during a full cycle. With the aid of surface analysis, the role of the cathode substrate and surface modification is demonstrated. The presented results are a further step toward a wise design of stable cathodes for Li–O2 batteries.
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| 6. |
- Qiu, Zhen, 1988-, et al.
(författare)
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Direct observation of active catalyst redox states and the effect of dynamically increased crystallinity on efficient alkaline water splitting
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Given the global increase in energy demand and serious environmental pollution, hydrogen fuel is a promising energy carrier to replace traditional fossil fuels due to its zero gas emissions and high energy density by weight. Electrochemical water electrolysis with non-precious metal catalysts offers a simple and cost-effective way for high purity and large-scale hydrogen generation. The realization of hydrogen evolution, however, is hampered by the large sustainable driving potential needed above the thermodynamic requirements. Here, we report dynamically crystallinity-enhanced (DCE) NiFe layered double hydroxide (LDH) ultrathin nanosheets, leading to faster electron transfer, smooth gas release ability, and more active surface areas, resulting in markedly improved catalytic efficiency. Compared with untreated NiFe LDH, DCE NiFe LDH exhibits much lower overpotential for the cathode reaction. Under 1 M KOH aqueous electrolyte, the bi-functional DCE catalysts require only 1.48 V and 1.29 V to reach 10 and 1 mA cm-2 in two-electrode measurements without iR-compensation, corresponding to 83% and 95% electricity-to-fuel conversion efficiency with respect to the lower heating value of hydrogen. In-situ Raman spectro-electrochemistry was carried out to obtain insight into the active catalyst phases, revealing the role of Fe and Ni and their function for OER and HER, respectively. The transformation from Ni(OH)2 to γ-NiOOH was clearly observed by in-situ Raman spectroscopy under OER operation. While, the Raman features of Ni(OH)2 and FeOOH were shown under HER process. It means the function of Ni and Fe is different under OER and HER, but it is noticeable that the observed Ni and Fe species at the different applied overpotential are dominant contribution to the catalytic activity. Our results shed light on the full understanding of overall water splitting in NiFe LDH ultrathin nanosheets and developing more efficient catalysts.
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| 7. |
- Qiu, Zhen, 1988-, et al.
(författare)
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In operando Raman investigation of Fe doping influence on catalytic NiO intermediates for enhanced overall water splitting
- 2019
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Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855 .- 2211-3282. ; 66
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal iron (Fe)-incorporated Ni oxide and oxyhydroxide compounds generally show an enhanced activity for alkaline water splitting. However, the role of Fe for this enhanced activity is not fully elucidated, especially under hydrogen evolution reaction (HER). Herein, we combine electrochemical and spectroscopic techniques to investigate the Fe doping effect on self-standing NiO nanosheets for enhanced activities for both HER and oxygen evolution reaction (OER) in overall water splitting. The results show that the presence of Fe suppresses Ni self-oxidation and adjusts the Ni–O local environment and its ability to form surface phases. In operando Raman spectroscopy is utilized to explore the active intermediates present under catalytic conditions. Apart from a slight suppression of grain size, our results show that Fe incorporation into NiO enhances in-situ formation of active layered intermediates NixFe1-xOOH with a phase transformation of FeOOH layers into γ-NiOOH layers containing Ni4+ at potentials approaching OER in contrast to undoped NiO electrodes with a dominating conversion of NiO to β-NiOOH, with persisting Ni3+. In addition, the work function on the electrode surface is reduced by 90 meV upon Fe doping, revealing a higher intrinsic Fermi-level and thus a lower requirement for added bias during HER. Together with the lower resistance for electron transport beneficial for both HER and OER, this leads to improved OER and HER efficiency upon Fe-doping. The study shows how Fe doping influences the active catalytic NiO intermediates for both HER and OER. Specifically, in operando vibrational spectroscopy utilized in parallel with electrochemical characterization can shed light on enhancement mechanisms and influence of doping for catalytic intermediates under any chosen bias at the respective electrode under full water splitting.
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| 8. |
- Qiu, Zhen, 1988-, et al.
(författare)
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Investigating the influence of iron on nickel oxide nanosheets for enhanced overall water splitting through in-situ Raman and impedance spectroscopy
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Mixed iron-nickel-based systems with tuned microstructure have recently emerged as promising non-noble electrocatalysts for alkaline water splitting. The understanding of interfacial reaction induced charge-transfer mechanisms and active phases, however, is still limited in overall water splitting. Herein, we report a detailed investigation of active surface phases and mechanisms during both the oxygen evolution (OER) and hydrogen evolution (HER) reactions in an alkaline electrolyte through in-situ Raman and impedance spectroscopy. The frequency response of electrical behavior is interpreted by a full theoretical equivalent circuit model and is related to the Raman spectra. The results show that the reaction resistance exhibits a strong dependence on applied bias and electrode materials in natural correlation with the reaction rate under both OER and HER process. The presence of iron (Fe) results in a less inductive feature observed in HER impedance spectroscopy, which is associated with the coverage relaxation of involved adsorbed intermediates. By in-situ Raman spectroscopy, it is clear to see that the main function of nickel (Ni) and Fe sites are dependent on the applied energy. When the Femi level shifts to more negative potentials, the hydroxyl groups are prone to adsorb on Fe3+ sites to form Fe oxyhydroxides, whereas the hydrogen groups show the tendency to adsorb (or migrate) to Ni sites, which accelerates water reduction and thus enhances HER activity. Moreover, the presence of Fe promotes the formation of high Ni valency (γ-NiOOH), leading to an improved OER catalytic performance. Our findings provide insights into the active phases formed in-situ under both the HER and OER reactions and are expected to be valuable for design strategies for efficient and earth-abundant Ni-Fe based catalytic systems.
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| 9. |
- Svensson, Fredric G., et al.
(författare)
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Rare-Earth-Modified Titania Nanoparticles : Molecular Insight into Synthesis and Photochemical Properties
- 2021
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:19, s. 14820-14830
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Tidskriftsartikel (refereegranskat)abstract
- A molecular precursor approach to titania (anatase) nanopowders modified with different amounts of rare-earth elements (REEs: Eu, Sm, and Y) was developed using the interaction of REE nitrates with titanium alkoxides by a two-step solvothermal-combustion method. The nature of an emerging intermetallic intermediate was revealed unexpectedly for the applied conditions via a single-crystal study of the isolated bimetallic isopropoxide nitrate complex [Ti2Y((PrO)-Pr-i)(9)(NO3)(2)], a nonoxo-substituted compound. Powders of the final reaction products were characterized by powder X-ray diffraction, scanning electron microscopy-energy-dispersive spectroscopy, Fourier transform infrared, X- ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence (PL). The addition of REEs stabilized the anatase phase up to ca. 700 degrees C before phase transformation into rutile became evident. The photocatalytic activity of titania modified with Eu3+ and Sm3+ was compared with that of Degussa P25 titania as the control. PL studies indicated the incorporation of Eu and Sm cations into titania (anatase) at lower annealing temperatures (500 degrees C), but an exclusion to the surface occurred when the annealing temperature was increased to 700 degrees C. The efficiency of the modified titania was inferior to the control titania while illuminated within narrow wavelength intervals (445-465 and 510-530 nm), but when subjected to a wide range of visible radiation, the Eu3+- and Sm3+-modified titania outperformed the control, which was attributed both to doping of the band structure of TiO2 with additional energy levels and to the surface chemistry of the REE-modified titania.
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| 10. |
- Zhou, Shengyang, et al.
(författare)
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Highly Crystalline PEDOT Nanofiber Templated by Highly Crystalline Nanocellulose
- 2020
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Ingår i: Advanced Functional Materials. - : John Wiley & Sons. - 1616-301X .- 1616-3028. ; 30:49
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Tidskriftsartikel (refereegranskat)abstract
- Abstract Packing conjugated conducting polymer chains into long-range order can significantly boost their carrier-transport properties, allowing the design and enhancing the performance of applications in next-generation flexible electronics, energy storage, etc. However, strategies for organizing molecular chains have hitherto been challenging and have been associated with poor reprocessability. This paper discusses the development and application of highly crystalline poly(3, 4-ethylenedioxythiophene) (PEDOT) nanofibers. These highly conductive PEDOT nanofibers possess well-defined quasi-one-dimensional topology combined with highly ordered molecular chain arrangements as a result of interface-induced morphological shaping followed by recrystallization induced by Cladophora cellulose. The nanofibers are also easily dispersible and able to be reprocessed in aqueous solution. The multiple functionalities of these PEDOT nanofibers are demonstrated by using them as building blocks for applications such as 1D assembled microfibers in an ultra-sensitive strain sensor, 2D papers for electrochemical energy storage, and 3D aerogels for simultaneous solar-thermal distillation and thermoelectricity generation. The methods discussed here can be the basis of a new avenue for regulating the molecular structure of, processing, and discovering applications for conjugated conducting polymers.
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